Ultrasonic imaging units containing a transmitter/receiver device of the above kind are known (German Offenlegungschrift No. 26 54 280, European Patent Application having the publication No. 0 006 197). The transmitter/receiver device provided in the known units, however, usually allows only one specific scanning process, e.g. a linear scan or a sector scan. However, for medical examinations in particular it is often advantageous to perform different scanning processes, and in fact such different scanning processes may be necessary to establish a diagnosis. Since the price of ultrasonic imaging units is relatively expensive, it is desirable to provide a transmitter/receiver device enabling different scanning processes, more particularly a sector scan and a compound scan, to be carried out with one and the same ultrasonic imaging unit. In order to generate high-quality images, this system should also comprise means for focusing the transmitted ultrasonic waves and, preferably, means for dynamic focusing of the reception characteristic. If the attempt were made to construct an apparatus of this kind simply by connecting together the means known in the art for performing the different scanning processes, and the electronic processing circuits used in such cases for the transmission signals and the echo signals, the size and the complexity of the circuitry required would be considerable. This would have two serious disadvantages: (a) the production costs of the apparatus would be drastically increased and (b) the large number of series-connected electronic components would have a very adverse effect on the signal-noise ratio and the image quality would be impaired correspondingly.
The object of the invention, therefore, is to provide a transmitter/receiver device of the kind indicated hereinbefore whereby with little expenditure it is possible to carry out different scanning processes, more particularly compound scan and sector scan, using substantially the same ultrasonic display unit, while producing high-quality ultrasonic images.